There is a general need for inexpensive energy storage for most electrical grids. Pumped-hydro energy storage is one of the least expensive methods of energy storage presently known. Pumped hydro-storage generally entails disbursing water from a higher elevation to a lower elevation when the production of electrical power is desired. The disbursed water may be provided to a turbine generator to generate electricity. Conversely, water may be pumped back to the higher elevation when the storage of energy is desired.
Some existing pumped-hydro energy storage may utilize an upper reservoir at the higher elevation and a lower reservoir at the lower elevation. These reservoirs may be connected by a pipe. When electrical power is needed from storage, water travels down the pipe and turns a turbine generation. Thus, in addition to possible inefficiency of the turbine and the pump, there may be frictional loss due to the passage of water through the pipe. In other existing pumped-hydro energy storage, the surface height of an upper reservoir may vary depending on the amount of water in the reservoir. Thus, a changing water height in the reservoir may result in changing hydrostatic pressure on the turbine generator, which may affect the efficiency of the turbine generator in producing electrical power.
Therefore, it would be advantageous to have a pumped-hydro energy storage apparatus and methods that do not have the one or more shortcomings described above.